1. Field of the Invention
The present invention relates to a nematic liquid crystal composition containing a 4-alkylbenzoic acid or a 4-alkoxybenzoic acid, particularly a nematic liquid crystal composition containing a mixture of a 4,alkylbenzoic acid with a 4-alkylcyclohexanecarboxylic acid to be used as a liquid crystal display device.
2. Description of the Prior Art
With the spread of a liquid crystal display device wherein use is made of the electrooptical effect of a liquid crystal, the development of a liquid crystal having properties suitable for these applications has been desired in the art. Properties required of the liquid crystal used in a liquid crystal display device are as follows.
(1) The chemical stability of the liquid crystal is high. PA1 (2) A liquid crystal phase is exhibited in a wide temperature range including room temperature. PA1 (3) A good response can be attained in a wide temperature range. PA1 (4) The matching with a driving circuit is good. PA1 (5) The optical anisotropy can meet an optical requirement.
However, no single-component liquid crystal compound capable of meeting all of the above property requirements is known in the art, and the present situation is that a liquid crystal composition comprising a mixture of several kinds of liquid crystal compounds is used for satisfying the above various property requirements.
Examples of known liquid crystal compounds used in the preparation of such a liquid crystal composition are phenyl ester compounds of cyclic carboxylic acids such as an alkyl- or alkoxybenzoic acid and an alkylcyclohexanecarboxylic acid, aromatic nitrile compound, an alkyl- or alkoxybiphenyl derivative, an alkyl- or alkoxyterphenyl derivative and an alkylcyclohexanecarboxylic acid.
Among these compounds, a 4-alkylcyclohexanecarboxylic acid is characterized by having a relatively low viscosity and a wide temperature range in which a liquid crystal phase is exhibited. It is known that liquid crystal compositions containing such a 4-alkylcyclohexanecarboxylic acid are excellent in various properties. In recent years, however, there is an ever increasing demand for a liquid crystal composition capable of meeting more strict property requirements. In particular, a lowering in the response speed is desired in the art. None of the above-described known liquid crystal compositions can meet the demand, however, and they cannot be satisfactorily put to practical use.
The most effective method of improving the response speed of a liquid crystal composition is to lower the viscosity of the liquid crystal composition. Since, however, the lowering in the viscosity should not be detrimental to other properties, the development of a method of lowering the viscosity of a liquid crystal composition without detriment to other properties has been desired in the art.